Iron metabolism

Iron Metabolism

Iron metabolism refers to the set of chemical reactions that maintain human homeostasis of iron at both the systemic and cellular level. Iron is an essential element for most life forms and is vital for many biological processes, including oxygen transport, DNA synthesis, and electron transport.

Overview

Iron is a critical component of hemoglobin, the molecule in red blood cells that carries oxygen from the lungs to the tissues. It is also a component of myoglobin, which helps muscle cells store oxygen. Iron is involved in various enzymatic processes and is essential for cellular respiration and energy production.

Iron Absorption

Iron absorption occurs primarily in the duodenum and upper jejunum of the small intestine. The process is tightly regulated to maintain iron homeostasis and prevent toxicity. Dietary iron exists in two forms: heme and non-heme iron. Heme iron, found in animal products, is absorbed more efficiently than non-heme iron, which is found in plant-based foods.

Mechanism of Absorption

1.Heme Iron Absorption: Heme iron is absorbed intact by enterocytes through the heme carrier protein 1 (HCP1). Once inside the cell, heme is degraded by heme oxygenase to release ferrous iron (Fe²⁺).

2.Non-Heme Iron Absorption: Non-heme iron must be reduced from ferric (Fe³⁺) to ferrous (Fe²⁺) form by the enzyme duodenal cytochrome b (Dcytb) before it can be absorbed. Ferrous iron is then transported into enterocytes by the divalent metal transporter 1 (DMT1).

Iron Transport

Once inside the enterocyte, iron can be stored as ferritin or transported into the bloodstream. Iron is exported from enterocytes into the bloodstream by ferroportin, the only known iron exporter. The exported iron is oxidized to ferric iron by hephaestin or ceruloplasmin and then bound to transferrin, the main iron transport protein in the blood.

Iron Storage

Iron is stored primarily in the liver, spleen, and bone marrow in the form of ferritin and hemosiderin. Ferritin is a soluble, easily mobilized form of storage iron, while hemosiderin is an insoluble form that is less readily available.

Regulation of Iron Metabolism

The liver-produced hormone hepcidin is the key regulator of iron homeostasis. Hepcidin controls iron levels by inhibiting ferroportin, thereby reducing iron absorption and release from macrophages. Hepcidin levels increase in response to high iron levels and inflammation, and decrease in response to anemia and hypoxia.

Disorders of Iron Metabolism

Disorders of iron metabolism can lead to either iron deficiency or iron overload.

Iron Deficiency

Iron deficiency is the most common nutritional deficiency worldwide and can lead to anemia, characterized by fatigue, weakness, and pallor. Causes include inadequate dietary intake, increased demand (e.g., pregnancy), and chronic blood loss.

Iron Overload

Iron overload can result from genetic conditions such as hereditary hemochromatosis, where excessive iron absorption leads to tissue damage. It can also occur due to repeated blood transfusions or excessive dietary iron intake.

Also see

• Hemoglobin
• Anemia
• Hepcidin
• Transferrin
• Ferritin